Hold-back elements in a forming-by-drawing machine



y 3, 1960 F. ANDERSON fi fi HOLD-BACK ELEMENTS IN A FORMING-BYDRAWING MACHINE Filed Jan. 16, 1958 5 Sheets-Sheet l y 1950 F.\ANDERSON 2,935,115

HOLD-BACK ELEMENTS IN; A FCRMINGBYDRAWING MACHINE Filed Jan. 16, 1958 I 5 Sheets-Sheet 2 F. ANDERSON May 3, 1966 HOLD-BACK ELEMENTS IN A FORMING-BY-DRAWING MACHINE 5 Sheets-Sheet 3 Filed Jan.

y 1960 F. ANDERSON 2,935,115

HOLD-BACK ELEMENTS IN A FORMING-BY-DRAWING MACHINE Filed Jan. 16, 1958 5 Sheets-Sheet 4 52 .fl 52 J y 60 F. ANDERSON 2,935,115

HOLD-BACK ELEMENTS IN A FORMING BY-DRAWING MACHINE HOLD-BACK ELEMENTS IN A FORMING-BY- DRAWING MACI-WE Frohman Anderson, Las Vegas, Nev. Application January 16, 1958, Serial No. 709,288

3 Claims. (Cl. 15332) This aplication is a continuation'in-part of application Serial No. 486,773, filed February 8, 1955, now Patent No. 2,851,080 which relates to a machine for shaping metal sheets into compound curves by pulling the sheets edgewise from one end to the other over a series of forming elements the working faces of which differ in contour transversely of the sheets and are disposed in stepped relation, a restraining or holdback force being exerted on the sheets in opposition to the pulling force to subject the sheets to stresses beyond their yield point. This operation in said parent application is termed formingby-drawing. a

Such machines are composed of three main functional components comprising the sheet forming structure, a draw bench including a power-actuated carriage for the mechanism that is to be translated in the performance of the operation, and the sheet pulling mechanism attached to and propelled by the carriage for gripping and drawing the sheets through the forming structure.

The sheet forming structure is composed of three stages through which the sheet progressively passes. The first stage has upper and lower portions which are relatively movable to and from each other and have opposing work engaging elements which provide a slot through which the sheet is drawn and which determines the general path of movement of the work sheet.

The second stage has a draw-over forming element mounted on a vertically movable ram and in operative position having its work engaging face, which is of diffcrent contour from the slot, disposed in stepped relation to the slot.

The third stage also has a draw-over forming element of the same contour as that of the second stage element and disposed in stepped relation thereto so as to engage the side .of the work sheet opposite that engaged by the second stage element.

This invention has to do with the first stage or holdv back work engaging elements. The character of the operation is such as to require that the hold-back elements may be caused to exert selectively a restraint upon the Work in the nature of a snubbing action which may vary indegree through a considerable range. Nor is the restraint or snubbing necessarily constant for a given work piece.

The invention contemplates upper and lower coacting opposing elements which intermesh in such a manner as to cause the work sheet to follow a sinuous or wavy path and be bent reversely as it is drawn through the zone of the opposing elements. The degree of flexing re- Since for a given alloy resistance to flexing is a function 9f the thickness and width of the sheets, it follows that for a given hold-backforce, less flexing is required for 2,935,115 Fatented May 3, 1960 ice relatively thick sheets and for relatively wide sheets than for relatively thin sheets and relatively narrow sheets. In other words, the opposing elements need to cause greater flexing to produce a given hold-back for thin sheets or narrow sheets than for thick sheets or wide sheets.

Specifically the hold-back elements are composed of a plurality of spaced cylindrical segments in succession which with the intervening hollows or valleys constitute their work-engaging surfaces. These segments are therefore in the form of cylindrical beads extending longitudinally of the elements, that is, transversely of the sheet in its direction of travel. The elements are disposed so that the beads on the two elements are staggered and those of the upper member oppose the valleys between the beads of the lower member. It therefore follows that the two elements when in surlicient proximity will cause the intervening sheet to be sinuously bent or defiected over the crest of the beads and conform to the curvature of the surfaces of the beads with more or less surface contact depending upon the height and radius of the bead. Preferably the lower element is maintained at a fixed height and the upper element is mounted on a ram which is raised and lowered, being first raised to admit the sheet and then lowered an amount to conform to the required spacing between the elements. If there are more than one bead on the upper element, they will preferably diminish in height from the front to the rear, while those on the lower element will be of the same height which is that of the feed table so that the sheet is level throughout when it is laid in position at the initiation of the operation.

If the thickness of the sheet varies from end to end the area of contact with the surfaces of the beads will need to vary during the draw in accordance with the variation in thickness. For example, some sheets taper from maximum thickness at one transverse edge to minimum thickness at the opposite transverse edge. To maintain a constant hold-back force throughout the draw of such taper sheets, the machine has means for dynamically varying the separation of the opposing holdba ck elements during the draw. If the taper is a diminishingthickness from the leading edge of the sheet, the separation of the two elements is gradually reduced during the draw, and vice versa.

'The invention will be understood from the following description of the embodiment of the invention illustrated in the accompanying drawings. 5

Fig. l is a side elevation of a complete machine embodying the invention;

Fig. 2 is a plan of the same;

Fig. 3 is a partial sectional view of the forming structure and of a portion of the draw bench structure taken on the line 3 3 of Figs. 2 and 4;

Fig. 3A is a fragmentary detail taken on line Zia-3a of-Fig. 3; r

Fig. 4 is a longitudinal central vertical section of the machine taken on line 4-4 of Fig. 3;

Fig. 5 is an enlarged vertical section of a portion of the forming structure on the plane of Fig. 4 and an end elevation of the draw head;

Figs. 6, 7, 8 and 9 are diagrams showing successive positions of the hold-back elements of the first stage.

The three stages of the sheet forming structure are contained between two uprights 11 and 12. The draw bench 13 is disposed at the outer side of upright 11 and consists of a U-shaped channel guide with a carriage l4 slidable therein. The sheet pulling mechanism includes an arm 15 secured to and extending laterally from the r i g n PPQ il -l a rew head 1. a g uto.-

3 matically operated jaws 17 for gripping the leading edge of the sheet.

The uprights 11 and 12 are secured to the base structure of the machine as shown in Fig. 3, and also mounted upon the base is a gear box 18 on whichrests the draw bench 13, its extending ends being supported by legs 19. A power motor 20 rests upon the base and has operative connection with gearing in gear box 18 for driving a bull gear 21 which meshes with a rack on the under side of carriage 14. Thus the motor reciprocates the carriage.

The arm 15 is supported on its outer end by leg 22 having a caster on its lower end which runs in a track in the supporting foundation.

The first, second and third stage forming structures are indicated in Fig. 4 by the designations 1st, 2nd and 3rd, respectively.

The lower portion of the first stage compirses a T- shaped body member having a cross head 23'and a rearwardly extending leg 24. This body member is supported in a cradle 25 which is universally mounted on a main base structure 26. For functional reasons not material to this invention the pistons of automatically operated hydraulic motors 27 (Fig. 3) are connected to the cradle 25 to adjust the first stage structure about longitudinal and vertical axes. Also, for functional reasons not here pertinent the first stage structure is movable dynamically toward and from the second stage by a hydraulic motor 28 which is operatively connected to the leg 24 by crank 29 and links 30. Secured upon the top face of the cross head 23 is the lower hold-back element 31 which extends the full length of the cross head and has a horizontal work-engaging face.

The upper portion of the first stage comprises a ram 32 which is a bar opposing the cross head 23. This first stage structure, both the upper and lower portions, is carried by secondary uprights 33 and 34 which have sliding engagement with the main uprights 11 and 12 through bearings 35 to permit the tilting and translating movement of the first stage through hydraulic motors 27 and 28. The cross head 23 has its ends attached to the secondary uprights 33 and 34. The ram 32 moves up and down in gibs 36 on the inner face of the secondary uprights. On the lower face of the ram 32 is secured the upper hold-back element 37. This upper hold-back element has a horizontal work-engaging face so that the slot between the two hold-back elements is a straight slot.

The ram 32 is raised and lowered through a toggle mechanism. Secured to and spanning the top ends of the secondary uprights 33 and 34 is a relatively fixed cross bar 38 which is adjustable in height between gibs 39 on the uprights 33 and 34. Two pairs of toggle links connect the bars 32 and 38. One pair is composed of links 40 and 41 which are of equal length. The other pair consists of link 42 which is pivoted on ram 32 and is of the same length as links 40 and 41, the link 43 which is pivoted to bar 38 and has an upward lever extension. As shown in Fig. 4, this link 43 is a double arm link, the rear arm being slightly wider than the front arm, as shown by dotted lines in Fig. 3. Also, as shown in Fig. 4, the bar 38 is hollow.

It is desirable to adjust the height bar 38 for sheets of different thickness, and for this purpose the ends of the bar are notched as shown at 38a and the gibs 39 are notched as shown at 39a. Blocks 44 are inserted on the bottom of notches 38a and shims are inserted on top of the blocks the thickness of which determines the upward limit of movement of bar 38. Also across and on top of the gibs 39 at each end is a bridge piece 45 which is bored to allow a screw 46 to pass therethrough and screw into a tapped hole in the top of bar 38 a distance which determines the downward limit of movement of bar 38.

The knuckle joints of the two pairs of toggle links are connected by bar 47. The upper end of the double link 43 extends above the bar 38 and is connected to the piston arm of hydraulic motor 48 which is supported on trunnions bearing in bracket arms 49 supported by and extending up from bar 38. The top ends of uprights 33 and 34 are rigidly connected by cross bar 50.

The operation of motor 48 is to raise and lower the ram 32 and hence the upper hold-back element 37 is automatically controlled through tracer cam mechanism which is fully described in said parent application. As will be later explained, the ram is raised by motor 48 through automatic or manually controlled switches to permit of the introduction of a sheet S, and the ram is then automatically lowered and the width of the slot between elements 31 and 37 is dynamically controlled during the draw.

The second stage structure comprises a ram 51 which extends between uprights 11 and 12 and is guided thereon by gibs (not shown). A draw-over forming element 52 is carried on the lower face of the ram with a workengaging face on its lower edge which is upwardly curved in its longitudinal dimension and which in operative position has its center below the slot between the hold-back elements of the first stage. The forming portion of this face is a ridge on its rear edge. The ram 51 is connected by toggles 53 to a cross bar 54 fixedly spanning uprights 11 and 12. The toggles are operated by bar 55 which is connected to the piston rod of hydraulic motor 56 mounted on upright 11 and automatically controlled through tracer cam mechanism as described in the parent application. A counterweight 57 is connected to the ram through levers pivoted on bar 54. As shown, the ram 51 is a double bar, the upper portion 51a of which is connected to bar 51 through turnbuckles 58, thereby enabling fine adjustments for the exactitude needed to compensate for variations in sheet thickness.

The third stage, like the lower body member of the first stage, comprises a T-shaped member having a cross head 59 spanning the uprights 11 and 12, and a rearwardly extending leg 60. This T-shaped member is slidably supported on the main base 26 and, for functional reasons not here important, it is dynamically adjusted longitudinally by a hydraulic motor 61 through the connection to the piston rod shown in Fig. 4. Secured to the cross head 59 is a draw-over forming element 62 which opposes the second stage forming element 52 and has on its upper edge a work-engaging face which is complementary to that of the second stage element and has a draw-over ridge on its front edge. The dynamic adjustment of this third stage structure by the motor 61 varies the distance between the work engaging ridges on the work faces of the elements 52 and 62.

To feed a sheet into the machine, the ram 32 of the first stage and the ram 51 of the second stage are raised and the sheet S is laid on the rearwardly extending feed table with its leading edge on the lower hold back element 31 and the third stage element 62 and projecting slightly in front of the second and third stage elements. The rams are then closed down and the arm 15 is brought up so that the jaws 17 can grip the edge of the sheet. The carriage 14 is then moved by the motor 20 to cause the jaws to pull the sheet from end to end through the forming structure.

The beads on the hold-back elements 31 and 37 have been mentioned. In form they are arcuate or semi-cylindrical extending parallel to the full width of the elements 31 and 37, the final bead being on the lower ele ment 31 when, as shown, the second stage is below the first stage, with the result that the sheet is bent over that final head as it leaves the first stage and then is reversely bent over the second stage forming element, being finally again reversely bent over the third stage to counteract to a controlled degree the unequal surface elongation at the second stage.

As shown more particularly in Figs. 6, 7, 8 and 9, the heads have rounded tops and are spaced somewhat more than the width or diameter of the beads immediately op posing the intervening spaces so that the sheet is not:

pinched between opposing heads when the two elements are at their closest approach. A proper set of the cam (not shown) which controls the vertical movement-of the upper element 37 will not allow the beads of one element to enter into the intervening spaces of the opposing element far enough to pinch the sheet between the tops of the beads and the bottoms of the hollows or valleys. The restraint is imposed by the reverse bending of the sheet over the successive beads, the degree of bending depending upon the height and curvature of the beads.

With the second stage forming element 52 below the exit slot of the first stage, which is the condition shown in the drawings, the last bead of the lower element 31 is in front of the last bead of the upper element and there are as many upper beads as there are valleys or intervening spaces in the lower element, the beads of the two elements being staggered so that those of each element oppose the valleys of the other element, as shown. While the upper element is shown as having two beads with an intervening valley and the lower as having two valleys opposing the beads of the upper element, and the diameter of all of the beads is shown as the same, the number of the beads and the diameter of the beads may vary.

The number and diameter of the beads depend upon the thickness and width of the sheet, and, generally speaking, more beads of lesser diameter are required for relatively thin and narrow material than for thicker and wider material.

Since to obtain a given hold-back force the degree of bend required varies inversely with the thickness of the material, it follows that the degrees of the segmental arc of the complete cylinder represented by each bead will be greater and the radius of curvature of the arc will be less for relatively thin sheets than for thicker sheets. That is to say, the beads will be higher and closer together and the valleys lower for the thinner sheets than for the thicker sheets.

Fig. 4 shows an upper element 37 with a single bead and a'lower element with a single opposing and complementary shape valley in the lower element 31. Figs. 5, 6, 7, 8 and 9 show twobeads on the upper element opposing two valleys in the lower element. It has been found that for material three-eighths of an inch or more in thickness, a single bead and valley combination sufiices, while for material .125 inch or less in thickness two or more beads and opposing valleys are to be preferred.

Before entering between the hold-back elements 31 and 37, the sheet passes between two opposing smoothing plates 63 and 64 which are on a level with the entrance end of the Work engaging faces of the respective holdback elements 31 and 37. The upper plate 64 is carried by and moves with the ram 32; The cam (not shown) in control of the operation of hydraulic motor 48 is set to limit the downward movement of the ram 32 so that in its operative position the plates 63 and 64 and the parallel faces of the respective hold-back elements at the entrance end of their opposing faces are spaced a few thousandths of an inch more than the thickness of the sheet being formed. These parallel faces are horizontal, the lower face 3111 being in the plane of the upper face of the plate 63 and of the tops of the beads on element 31, while the face 37a is disposed at the level of plate 64 intermediate the bottoms of thevalleys and the crests of the beads of element 37 so as to cooperate with its opposing face 314: to limit the approach of the two elements to a point where the sheet is not pinched'between the opposing beads and valleys. Thus the sheet is not pinched either between the smoothing plates or the hold-back elements. However, the sheet is directed in a definite plane into the beaded or holdback zone where it is subjected to the reverse bending.

The width of the valleys exceeds the diameter of the respective opposing beads by at least the thickness of h the sheet on each side of the bead, and the level of the face 37a relative to the upper beads is such that the face 37a cooperates with face 31a to leave ample clearance between the crests of the beads and the bottoms of their opposing valleys for the sheet being drawn between the elements in the nearest approach of the elements.

The hold-back force is a function of the stiffness of the sheet or, in other words, its resistance to bending. The stiifness of the sheet or its resistance to bending varies directly with the width of the sheet and directly as the cube of its thickness.

if two or more beads exist on the face of the upper element 37, they may diminish in height from the front toward the rear. For example, it has been found satisfactory in practice that for .025 inch aluminum alloy metal the upper element has five beads of seven-sixteenths of an inch in diameter but decreasing in height from seven-sixteenths of an inch for the front or last head to three-sixteenths of an inch for the first or rear bead in the direction of draw. The lower element of course will also have five beads all of the same diameter and height, for example, seven-sixteenths of an inch in diameter and height with their crests on the level of the lower smoothing plate 63.

For metal .040 inch in thickness it is satisfactory to have three beads on each element ten-sixteenths of an inch in diameter with those on the lower element and the front one on. the upper element twelve-sixteenths of an inch in height, and the middle head of the upper element eight-sixteenths of an inch in height and the rear bead five-sixteenths of an inch in height, the height being measured from the root of the bead.

For .051 inch thick metal stock it has been found satisfactory to have two beads on each element which are thirteen-sixteenths of an inch in diameter, those on the bottom and the front top bead being fourteen-sixteenths of an inch in height and the rear top bead being tensixteenths of an inch in height.

For. .063 inch metal thickness it is satisfactory to have two beads one inch in diameter seventeen-sixteenths of an inch in height for all except the rear top bead which is eleven-sixteenths of an inch in height.

For .125 stock it is satisfactory to have two beads on each element approximately two inches in diameter with those on the lower element one inch in height and the front bead on the upper element approximately thirteensixteenths of an inch in height and the rear bead approximately ten-sixteenths of an inch in height.

It is the overlap of the top and bottom beads which determines the degree of reverse bending of the sheet in passing through the hold-back zone. It is possible, even for the thinner stock, by proper proportioning or the height and diameter of the beads, to obtain the requisite hold-back force with two beads per element. For example, for .032 stock twobeads of eight-sixteenths of an inch diameter on each element has proven satisfactory with those on the lower element and the front bead in the upper element approximately five-sixteenths of an inch in height and the rear bead on the upper element approximately four-sixteenths of an inch in height.

As shown in Figs. 6, 7, 8 and 9, it is desirable, especially for the thinner stock, to provide a longitudinal groove 37b in the upper element opposite the line of first bend to afford a relief or space for the metal in that line.

The above examples assume uniformity of width of the sheets. Within limits the dimensions of the beads given above are appropriate for various widths of sheets, but it will be understood that since the stifiness is in part a function of the width of the sheets, for extreme variations in width it might be desirable to compensate for variations in stiffness by variations in the dimensions and even the number of the beads.

Above a certain thickness of sheet, the degree of stiffness I is such that a single reverse bend will afford the requisite hold-back. In such case but a single bead and valley on each element will suffice. With such profile of holdback face, the valleys are concentric with the opposing beads when the elements are in operative relation.

The radius of curvature of the beads and valleys in creases with the thickness of the sheets. For example, for three-eighths inch stock, each element may have a single bead of 2.4 inch radius. The faces of the two elements are symmetrical and are spaced approximately eleven-sixteenths of an inch in operative position.

Similarly for one-half inch stock, a single bead and valley on each element suffices but the radius of the heads is increased to 3.2 inches with the opposing valleys concentric with the faces of the heads, the spacing of the symmetrical opposing faces being the same as with threeeighths inch stock. The beads therefore have a lesser curve and the radius of bending of the stock is easier. The bending moment is however approximately the same in the two cases, and hence the reactive or hold-back force is approximately the same.

For nine-sixteenths inch stock, the radius of curvature of the beads is preferably approximately 3.59 inches. The area of contact of the sheet ,with the face of the beads increases, of course, with an increase in radius, the angle of contact remaining constant or substantially so.

Figs. 6, 7, 8 and 9 illustrate diagrammatically the several positions of thecooperative hold-back elements. These figures show two beads and two intervening valley elements. Fig. 6 shows the sheet feeding position with the upper element raised and the sheet S laid in position with the leading end around the second stage element 52 and the'leading edge in position to be seized by the jaws. Fig. 7 shows the upper element lowered to the position where the front bead contacts the sheet and flattens it down into contact with the two beads on the lower element and its flat entrance face. In Fig. 8 the further downward movement has caused the front bead of the upper element to depress the sheet somewhat into the opposing valley, while the rear shorter bead just contacts the sheet. In Fig. 9 the final position is shown in which the sheet is given a double reverse bend of lesser degree in the rear valley'than in the front. The rear fiat face portions of the two elements appear to contact the sheet but in reality clear it by a few thousandths of an inch, as above stated.

The amount of diiferential stretch of the sheet is of course a function of the degree of hold-back and for this reason less hold-back is required for drawing shallow curves than for drawing deeper curves. It is therefore apparent that the dimensions of the beads and the amount of overlap and hence the degree of flexing of the sheet and the area of surface contact of the sheet with the beads will be varied in accordance with the desired degree of hold-back.

It will be understood that the principle of the invention is independent of the precise form of construction 8 illustrated in the drawings and above particularly described to effect the reverse bend of the sheet as it is drawn, and that 'oth'erconstructions for this purpose will readily occur to those skilled in the art within the principle and scope of the invention as defined in the following claims. I

What is claimed is:

1; In "a forming-by-drawing machine having means to pull asheet edgewise, hold-back means comprising, in combination with a pair of opposing horizontal smoothing plates disposed on opposite sides of the path of the sheet, a pair of opposing elements immediately adjacent the said plates and constituting a hold-back zone, the said elements having complementary opposing faces each consisting of a fiat entrance portion and spaced semi-cylindrical beads with intervening valleys, the beads of one element opposing the valleys of the other element and the width of the valleys exceeding the diameters of their respective opposing beads, the flat entrance portions being in the planes of the smoothing faces of the respective plates and the fiat portion of one element being in the level of the crests of the beads of that element and the I flat portion of the other element being at a level intermediate the bottoms of the valleys and the crests of the beads of that element, whereby the flat portions cm operate to maintain clearance between the beads and valleys at the closest approach of the elements, and means to move one of the elements and its respective smoothing plate toward andfrom the other element and plate and to position the movable element with the beads overlapping with respect to the path of the sheet.

2. In a forming-by-drawing machine having means to pull a sheet edgewise, hold-back means as defined in claim 1 in which the movable element has the fiat portion at the said intermediate level and has a plurality of beads which diminish in height from the front bead to the rear bead.

3. In a forming-by-drawing machine having means to pull a sheet edgewise, hold-back means as defined in claim 1 in' which the element having a bead immediately adjacent its fiat portion has a relief groove connecting the flat. portion to the bead.

References Cited in the file of this patent UNITED STATES PATENTS 1,066,849 Ryden July 8, 1913 1,544,320 Hough June 30, 1925 1,917,624 Webb July 11, 1933 2,480,826 Anderson Sept. 6, 1949 FOREIGN PATENTS 320,511 Germany Apr. 23, 1920 69,985 Holland May 15, 1952 

